1. Field of the Invention
The present invention relates to an apparatus for controlling a tracking of a tape for a 8 mm VCR (Video Cassette Recorder) or a DAT (Digital Audio Tape) to align a recorded signal track of the tape with a head of a rotating drum of the VCR or the like.
2. Description of the Prior Art
A tracking apparatus of the prior art is of a type as shown in FIGS. 1 and 2, in which a tape(2) is brought into contact with a rotating drum(3) by means of tape traveling guide rollers(1a,1b) and traveling of the tape(2) is effected by means of a capstan shaft(4) and a pinch roller(5), both of which are operated at its downstream portion. Such a prior apparatus carries out a first mode of a recording operation in which signals are recorded on the tape, and a second mode of a playback operation in which a head of the rotating drum follows a recorded track of the tape.
In the playback operation mode, there may be occurred depending upon a traveling condition of the tape a state in which the track(11) of the tape(2) precedes the head(10) of the rotating drum, as shown in FIG. 6a, or another state in which the track(11) lags behind the head (10), as shown in FIG. 6c. In this manner, when the head(10) and track(11) are not aligned with each other, as in the states shown in FIGS. 6a and 6c, in contrast to that shown in FIG. 6b, in which the two are in registrer, a picture noise or a picture trembling phenomenon is generated. Therefore, in this case, a tracking control of the prior art for aligning the track(11) of the tape with the head(10) of the rotating drum, as shown in FIG. 6b, is carried out by, when the track(11) precedes the head(10), as shown in FIG. 6a, reducing a rotational speed of the capstan shaft which functions to transport the tape, and when the track(11) lags behind the head(10), as shown in FIG. 6c, increasing the rotational speed of the capstan shaft. On the other hand, in the record operation mode, the capstan shaft(4) is interlocked to the rotating drum(3) through a phase servo mechanism to transport the tape in synchronism with the rotation of the drum. In the playback and recording modes, the rotating drum(3) always rotates at a constant speed.
In the prior apparatus in which an alignment of the track of the tape with the head of the rotating drum is accomplished by controlling the rotational speed of the capstan shaft as discussed above, a motor for driving the capstan shaft must have an excellent control characteristic. The control characteristic, however, highly depends upon a rotational speed of the motor, so that controllability of the motor becomes deteriorated in a low speed mode. Further, the control action is slow due to high inertia of the capstan shaft itself connected to the motor.